This application claims the priority of German Application No. 198 31 733.6, filed Jul. 15, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a motor vehicle having an electronically controlled automatic transmission, which comprises a parking position, and a power parking brake.
From German Patent Document DE 39 29 286 A1, an automatic transmission for motor vehicles is known, in the case of which the individual driving positions, such as P, R, N and D, are engaged in an electronically controlled manner. In this case, an operating element for selecting the individual driving positions is no longer mechanically connected with the transmission, but rather acts only as an electric switching element for selecting the desired driving position. When the operating element is operated, electric contacts are closed. The closed contacts generate switching pulses which are processed by an electronic control unit and are converted to corresponding commands issued to the control elements for the driving position selection and for the shift control. If driving position P (parking position) is selected by means of the operating element, control elements in the form of a locking device are activated in order to set a parking position.
From German Patent Document DE 196 25 019, an electronically controlled automatic transmission is known which automatically sets a parking position as a function of certain operating conditions, for example, when the driving speed of the motor vehicle is equal to zero and the ignition circuit was opened by means of the ignition key. Here also, a locking device in the form of a solenoid acting as an actuator is used.
From U.S. Patent Document U.S. Pat. No. 4,892,014, an electric control for an automatic transmission is known. Here, a control unit automatically activates a power parking brake if the parking position had previously been engaged. The parking brake will then automatically be released again if a number of conditions have been met.
In the case of these known electronically controlled automatic transmissions, a problem may exist if either the parking position or the power parking brake becomes inoperable or fails.
Therefore, it is an object of the invention to provide a motor vehicle with an electronically controlled automatic transmission and a power parking brake wherein the function of the parking position or of the power parking brake can also be carried out when the corresponding system fails.
This object is achieved by a motor vehicle having an electronically controlled transmission system with a parking position function and a power parking brake system. Both systems are checked by a checking device and, in the event an operational failure of one system is detected, the function of this system is taken over by the other system. In particular, the transmission may be controlled by an electric transmission control and the power braking brake may be controlled by a control unit. Both control units may be part of the checking device and therefore connected to each other.
The object is also achieved by a method comprising the checking of one of the parking position function of the transmission system and the power parking brake system and, in the event of failure of one system, operating the respective other system to take over the function of the failed system.
Advantageous further developments of the invention are described herein.
According to the invention, both the parking position as well as the power parking brake represent systems which are redundant with respect to one another. In the event of a failure of one system, its function can be taken over by the respective other system. As a result, the motor vehicle is in every case secured against rolling-away. In addition, in this manner, the entire functionality range which is provided by these two systems can continue to be ensured in the normal operation. If one system fails, the respective other system takes over its function. The driver does not have to think about whether he has to secure the vehicle by means of the parking position or the power parking brake.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.